Poly (1 3 4-oxadiazoles) and their synthesis

ABSTRACT

NORMALLY SOLID POLY(1,3,4-OXADIAZOLES) CAN BE PREPARED BY THE CYCLODEHYDRATION OF N,N&#39;&#39;-BIS(ISOMALEIMIDE). POLYHYDRAZIDES. THESE PRODUCTS ARE CHARACTERIZED BY THEIR THERMAL STABILITY AND HIGH MELTING POINTS.

.imide). polyhydrazides. These products are characterized 3,632,560 Patented Jan. 4, 1972 Preferred temperatures for the thermal cyclodehydra- 3,632,560 tion are about 80 to 300 C. although higher tempera- POLY (1,3,4-XADIAZOLES) AND THEIR tums can be used if desired SYNTHESIS The preferred temperature range for chemical cyclo- You-Ling Fan, East Brunswick, N.J., assignor to Union Carbide Corporation, New York, N.Y. No Drawing. Filed Jan. 29, 1969, Ser. No. 795,076

Int. Cl. C07d 85/54 US. Cl. 26078.4 R Claims ABSTRACT OF THE DISCLOSURE Normally solid poly(1,3,4-oxadiazoles) can be prepared by the cyclodehydration of N,N'-bis(isomaledehydration is about 150 to 250 C. although other ranges such as 80 to 150 C., 100 to 300 C. or 250- to 350 C. can be use if desired.

The inert atmosphere used with the thermal cyclodehydration is readily supplied by conducting the reaction under such gases as argon, krypton, Xenon, or nitrogen and the like.

The preferred dehydrating agents when the cyclodehydration of the polyhydrazides is carried out chemically are polyphosphoric acid and phosphorous pentoxide.

- Other dehydration agents which can be used include by thermal stablhty and hlgh meltmg pomts' thionyl chloride, phosphorus oxychloride, trifluroacetic anhydride, acetic anhydride and the like. When phos- This invention relates to poly(l,3,4-oxadiazoles) and to phorus pentoxide is employed it is preferred to use an their synthesis from N,N'-bis(isomaleimide) polyhyamine such as triisopropyl amine, triisobutyl amine and drazides. the like in conjunction with it.

It has been found that polyhydrazides prepared by the polymerization of equimol'ar quantities of N,N-bis(isomaleimide) and dihydrazides as well as those prepared by the low temperature solution condensation polymerization of N,N'-bis(isomaleimide) dihydrazide adducts and a diacyl chloride can be cyclodehydrated to poly(l,3,4- oxadiazoles) having a repeating unit represented by the formula:

The chemical cyclodehydration can be carried out in conventional equipment well known in the art including glass vessels, glass lined vessels, stainless steel vessels and the like.

The thermal cyclodehydrations can be effected by any type of heating equipment operable in the desired temperature range.

Pressure is not narrowly critical in either cyclodehydration technique although atmospheric pressures are preferred for economic reasons.

The progress of the cyclodehydration of polvl drazides can be followed at successive stages of the reaction by infrared spectroscopy by the disappearance of the -NH stretching band (about 3200 cmr and the amine I hand (about 1650 cm. which are characteristic of the hydrazide group and the appearance of new absorption bands (at about 1720' to 1430 cm. due to the formation of the 1,3,4-oxadiazole ring.

where R and n are as defined above.

drazides can be represented as follows:

i I. i i i i a i [3NHNH- 3 (3-NHNHC-R- NHNHC-RCNHNH \CH=GH CH=OH n C\ /C\ /C\ /O\ /C\ /C-RC\ /C-R \NN/ CH=CH \NN/ CH=CH \NN/ n wherein R, R' and n are as defined previously. The poly(1,3,4-oxadiazoles) containing alkylene radi- In each case the cyclodehydration can be effected either cals, represented by R or R, are dark brown solids which soften at about C. and melt at temperatures below those of the precursor polyhydrazides.

thermally in an inert atmosphere or chemically by contacting the polyhydrazide with a dehydrating agent.

The poly(1,3,4-oxadiazoles) containing arylene radicals, represented by R or R, soften at about 300 C. but show no evidence of melting below about 310 C.

Both types of poly(1,3,4-oxadiazoles) are insoluble in common organic solvents including ketones such as acetone, methylethyl ketone, hexanone-2, diisopropyl ketone or cyclohexanone; alcohols such as methanol, ethanol, isopropanol, or cyclohexanol; aliphatic hydrocarbons such as hexane, heptane, or octane and aromatic hydrocarbons such as benzene, toluene, xylene and the like.

The po1y(1,3,4-oxadiazoles) of this invention can be used in the fabrication of fibers and formed articles as well as adhesives, sealants and coating materials.

The invention is further described in the examples which follow. All parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 Preparation of ply(1,3,4-oxadiazole) by thermal cyclodehydration of a polyhydrazide.

A polyhydrazide derived from sebacic acid and N,N'- bis(isomaleimide) having repeating units which can be represented as:

and a reduced viscosity of 0.42 (when measured at a con- 4 EXAMPLE 2 Example 1 was repeated with the exception that the polyhydrazide was exposed to a temperature of about 180 C. for 120 minutes. The dark brown solid poly(1, 3,4-oxadiazole) recovered had a reduced viscosity of 0.09 (when measured at a concentration of 0.2 gram in 100' m1. of sulfuric acid at 25 C.) and a melting point range of about 183 to 210 C.

EXAMPLE 3 Preparation of poly(1,3,4-oxadiazole) by cyclodehydration of a polyhydrazide with polyphosphoric acid.

A three-necked 100 ml. flask, equipped with a mechanical stirrer, condenser, thermometer and nitrogen inlet tube was charged with 20 ml. of polyphosphoric acid. The flask and contents were heated to about 200 C. and 1.2 grams of the polyhydrazide described in Example 1 was added in the form of finely divided particles. This mixture was stirred for 3 hours at 200 C. Poly(1,3,4-oxadiazole) was isolated by pouring the reaction mixture into an excess of ice water, filtering, washing in a Waring Blendor with water and filtering again. The dark brown solid having the repeating units delineated in Example 1 was dried in a vacuum oven at 70 C. This product had a reduced viscosity of 0.12 (when measured at a concentration of 0.2 gram in 100 ml. of sulfuric acid at 25 C.) and a melting point range of about 186-3l0 C.

EXAMPLE 4 Example 3 was repeated with the exception that the reaction time at 200 C. was 3 hours instead of 2 and 1.2 grams of a normally solid polyhydrazide was used having repeating units which may be represented as:

The dark brown solid poly(1,3,4-oxadiazole) recovered centration of 0.2 gram in 100 ml. of dimethyl sulfoxide had a reduced viscosity of 0.09 and a melting point of at 25 C.) was placed on a ceramic disk in finely divided form and transferred under an argon atmosphere into a quartz tube mounted in a Hoskins furnace preheated to a temperature of 300 C. As cyclodehydration took place water condensed at the outer sections of the qaurtz tube, after a period of exposure of 0.5 minute. The disk and product were removed from the furnace and cooled to room temperature in an argon atmosphere.

The product was a dark brown solid having a reduced viscosity of 0.085 (when measured at a concentration of about 300 C. The product having the repeating units:

showed an elemental analysis for oxygen as follows:

Calculated for C H N O (percent): 0, 12.90. Found (percent): 0, 12.01.

EXAMPLE 5 Preparation of poly(1,3,4-oxadiazole) by cyclodehydration of a polyhydrazide with phosphorus pentoxide.

A three-necked 100 ml. flask, equipped with a mechani cal stirrer, condenser, thermometer and nitrogen inlet tube 0.2 gram in m1. of sulfuric acid at 25 C.) and a t charged Wlfh g- 111016) of phosphorus pentmelting point range of about 180 to 210 C. oxide and 40 ml. of triisopropyl amine. This mixture was This product was poly(1,3,4-oxadiazole) having repeatheated to reflux (about C.) affording a browning units which may be represented as: colored slurry. Finely divided particles (1.2 grams) of l /O\ /O\ -o /C\ o /o C(OH;)g- L NN 0H=0 N-N CH=CH N-N J to the flask with stirring and refluxing continued for 2 hours. The brown solution which resulted was cooled to room temperature and successively extracted with dimethyl ether and water to remove unreacted reagents and 5 phosphoric acid. The product, poly(l,3,4-oxadiazole) was 5 6 the polyhydrazide described in Example 1 were charged washed with water and acetone, filtered and dried in a 4. Poly(1,3,4-oxadiazo1e) claimed in claim 1 wherein vacuum oven at 70 C. This polymer had a reduced vis- R is cosity of 0.09 and a melting point of about 300 C. k

Although the invention has been described in its pre- 10 ferred forms with a certain degree of particularity, it is Q understood that the present disclosure has been made only by way of example, and that numerous changes in the details may be made without departing from the spirit and Y( Clailmd in claim 1 wherein scope of the invention. R is What is claimed is:

1. Normally solid poly(1,3,4-oxadiazoles) having repeating units represented by the structure:

0 O 0 0 I 0 0\ /0 0\ /0 ORC\ 2pm L\ \N-N/ CH=CH \NN/ CH=CH \NN/ N-N 1.1-

wherein R is a divalent hydrocarbon radical selected from References Cited the group consisting of alkylene radicals having 1 to about UNITED T T PATENTS 18 carbon atoms and phenylene radicals, R is a phenylene 2,765,304 10/1956 Slegnst 6t 31 260 240 radical and q is an integer having a value of 0 w 1. OTHER REFERENCES 2. Poly(1,3,4-oxadiazole) claimed in claim 1 wherein Frazer et Chemical Abstracts, 60, 12120 R is (CH Iwakura et al., Chemical Abstracts, col. 9029 (1966). 3. Poly(1,3,4-oxad1azole) claimed in claim 1 wherein 35 R is JOHN D. RANDOLPH, Primary Examiner 

